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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * under the terms of the GNU General Public License version 2 only, as
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 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package sun.jvm.hotspot.gc.shared;

import java.util.*;

import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.types.*;

/** A space that supports compaction operations.  This is usually, but
    not necessarily, a space that is normally contiguous.  But, for
    example, a free-list-based space whose normal collection is a
    mark-sweep without compaction could still support compaction in
    full GC's. */

public abstract class CompactibleSpace extends Space {
  private static AddressField compactionTopField;

  static {
    VM.registerVMInitializedObserver(new Observer() {
        public void update(Observable o, Object data) {
          initialize(VM.getVM().getTypeDataBase());
        }
      });
  }

  private static synchronized void initialize(TypeDataBase db) {
    Type type = db.lookupType("CompactibleSpace");

    compactionTopField = type.getAddressField("_compaction_top");
  }

  public CompactibleSpace(Address addr) {
    super(addr);
  }

  /** May be used temporarily during a compaction phase. */
  public Address compactionTop() {
    return compactionTopField.getValue(addr);
  }
}
